I have bulk 7.62x54R in spam cans and in their original wooden crates for long term storage of it. I also have 9mm, 5.56 and 7.62x39 in spam cans as well for long term storage. For calibers that cannot be obtained in spam cans, I use 30mm military ammo cans, I can get as many as I want for $6 a piece at my LGS. I clean the ammo cans out, inspect the rubber gaskets, apply a thin coat of silicon to the seal and put in a handful of diseccant packs as well as oxygen absorbing packs. The silicon provides an airtight seal, the diseccant gets rid of any moisture and the oxygen absorber removes all oxygen from the can. Oxygen is what actually causes condensation to form from temperature changes. I have a location where I store all my mid to long term ammo that has a stable environment and is out of sight. By vacuum sealing the ammo cans in this manner I do not need to worry about changing out the desiccant as once the original moisture content is removed the lack of oxygen stops any further moisture from being present. Has worked well for me for years without any issues.